In a nutshell, it takes 1 – 3 days to get into ketosis.
Switching to fat-burning mode is a process that takes many steps to complete. For your body to enter ketosis, it needs to do the following.
1. Deplete its glycogen
When you stop eating carbs, blood glucose levels drop and your body turns to liver glycogen (the stored form of glucose) to help raise your blood sugar.
2. Break down fats
Your insulin levels drop in response to low carbohydrate availability. This drop triggers the breakdown of fatty acids as well as their uptake in liver mitochondria (cell organelles).
3. Start making ketones
Within the next few days, your liver will start making ketones to meet your body's growing energy demands. The brain is dependent on a constant influx of fuel, so it will be using up most of the ketones made.
If you remain under your optimal net carbs limit, then you should enter ketosis within 2 to 3 days. But it can take up to 7 days. The fastest way to get into ketosis is to exercise on an empty stomach, in order to accelerate the depletion of glycogen in your body. You can also do a Fat Fast for a few days (eating more fat) to speed up the rate at which you enter ketosis AND start to cut out refined carbs (like sugar) before you go for full ketosis. Another option is to do a water fast, (only drinking water) which also speeds up getting into ketosis.
Ketosis is the main goal of keto. When your body switches to this metabolic state, it starts utilizing ketones instead of glucose for fuel. Being in ketosis comes with benefits like weight loss, reduced risk of disease, and mental clarity.
The time it takes to enter ketosis varies from one person to the next. You can enter ketosis quicker or later depending on your body composition, diet, and activity levels. However, there are averages and limits you should know about.